Mars Global Surveyor
Mars Orbiter Camera

Mars Shoreline Tests: Contact between Cydonia and Acidalia Planitia

MGS MOC Release No. MOC2-181, 1 October 1999

The picture above left shows the regional context of a Mars Global
Surveyor (MGS) Mars Orbiter Camera (MOC) high-resolution image that
was targeted in August 1998 with the intent to test the hypothesis that
the northern plains of Mars were once the site of a vast ocean of liquid
water. The picture on the right shows the resulting MOC image, numbered
SPO2-515/05 and located at 40.0°N, 6.0°W in the transition zone
between the Cydonia region and Acidalia Planitia, Mars.

The context image on the left includes several dark lines, some of which
are labeled I and some are labeled G. These dark lines
were proposed in previous, peer-reviewed scientific papers to be possible
ocean shorelines located along the margins of the martian northern plains.
Line I was called the "Interior Plains Boundary," and line G
was called the "Gradational Boundary." The MGS MOC high resolution image
was targeted such that it would examine the nature of line I, the
Interior Plains Boundary.

The figure on the right shows the MOC high resolution view. The picture on
the left side of the figure is the full MOC image and the white box indicates
the location of the expanded view to the right. In the expanded view (the
center of the figure on the right), the location of line I--the
proposed shoreline--is shown by a dashed curve. The dashed curve follows
a subtle, shallow trough. None of the types of coastal landforms common
on Earth--such as a beach, wave-cut cliff or terrace, or coastal dune fields,
are seen at this location. If an ocean had once been present, then the water
would have covered the top 2/3 of the expanded view--i.e., water
would have lapped up against the
rounded mounds in the lower 1/3 of this picture. Instead of coastal landforms,
the MOC image exhibits a dark surface in its upper 1/3. The dark surface
covers older, rounded hills and has a low, lobate escarpment along its
southern margin.
This escarpment faces south--that is, it faces toward the once-proposed
coastline. In other words, the escarpment faces in a direction opposite
of what would be expected for a coastal environment.

The contex picture uses Viking orbiter image 561a24 as a base. This
Viking image is illuminated from the left.
For a higher-resolution view of the context image (870 Kbyte),
CLICK HERE.

The MOC high resolution image is illuminated from the left/upper left.
For a higher-resolution view of the narrow angle camera figure (485 Kbyte),
CLICK HERE.

For additional MOC image tests of proposed martian shorelines,
see the following:

Malin Space Science Systems and the California Institute of Technology
built the MOC using spare hardware from the Mars Observer mission. MSSS
operates the camera from its facilities in San Diego, CA. The Jet Propulsion
Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor
spacecraft with its industrial partner, Lockheed Martin Astronautics, from
facilities in Pasadena, CA and Denver, CO.